What are some tools for labelling images and videos?
There are a few.


Sloth
LabelBox
RectLabel
LabelMe


OpenCV also has some facilitation for annotating.

Annotation is the more common name used in software suites for tools that facilitate adding labels to images and frames of movies because.  Simple categorization is of limited use in the real world, especially with moving pictures where action may be important and requires recognizing consistent position and size change.

Annotation is more than adding a number or concept class instance in object recognition. There are five numbers that define the frame, potentially seven if both certainty and pixel depth layers are independently annotated as in the case of heat signatures.


$h_0$: Box horizontal min
$h_1$: Box horizontal max
$v_0$: Box vertical min
$v_1$: Box vertical max
$t$: Time or frame index
$P$: Optional probability that the object in the box qualifies if the annotation involves doubt
$\lambda$: Optional pixel layer depth indicating range of wavelengths, important for discriminating warm blooded people and pets from immobile objects for vehicle automation or the heat signatures to discriminate ballistic missiles from benign aeronautics